This invention relates to composite packaging materials, typically multiple layer packaging materials. This invention further relates to certain coated sheets used in making such composite packaging materials, and methods of making such coated sheets and composite packaging materials.
A wide variety of generally dry particulate products are packaged typically in bulk quantities in multiple layer flexible packaging materials based primarily on paper, and optionally including one or more polymeric layers. Such multiple layer flexible packaging materials typically have a coated outer layer wherein the coating is suitable for receiving conventionally-available inks printed as graphics and other indicia of the product contained therein and wherein such outer layer is so-printed at such coating. Effective employment of the packaging requires effective maintenance of such printing on the outer surface of the package throughout the period when the product is contained therein. Effective employment of the packaging further requires that indicia and other images so printed on the outer surface of the packaging material not be substantially degraded by flexing of the packaging material during normal use of the packaging material in containing such product.
Dry particulate products typically packaged in packaging of the nature being addressed herein comprise a variety of contained liquidous components such as especially oils and water, as well as certain components which are potentially chemically reactive. Further, certain such products are also abrasive such that the packaging material must be sufficiently tough to not be deleteriously degraded by abrasion imparted by such contained products.
Any one such product may contain no such liquidous, chemically reactive, or abrasive components, may contain only one such component, or may contain multiple such components. Such liquidous components and chemically reactive components, along with any abrasive properties, hold potential for damaging certain elements of the packaging material if such elements of the packaging material are exposed to such components.
Examples of such dry particulate products are salt, sugar, dry pet foods which contain various oils, flour which contains grain oil, cement and grout which contain reactive calcium compounds, bird seed which contains various seed oils, and various grains which contain grain oils. In general, the size of the particles of the contained product is of little consequence to employment of the instant invention.
Typical packaging materials of interest in the invention are used to package product in bags which contain relatively larger quantities of at least 1 pound, but more commonly at least 4 pounds. Respectively stronger ones of packaging materials of interest in the invention are used to make bags which contain e.g. 25 pounds, 50 pounds, and up to 100 pounds or more of product.
A typical conventional packaging structure of the nature being addressed herein has a first outer layer of sheet material which contains printed indicia thereon, and at least one interior strength layer, which is typically an unbleached kraft paper layer. In many implementations, the packaging structure further comprises a polymeric, e.g. polyolefin, layer such as a polypropylene layer or a polyethylene layer disposed on the interior of the packaging structure. Typically, the kraft strength layer is between the outer layer and the polymeric layer. However, it is within the scope of the invention that the polymeric layer be between the kraft strength layer and the outer layer. Further, and especially where a relatively greater mass of product is to be contained in a bag, more than one strength layer can be used in the packaging structure, interiorly of the outer layer.
Such conventional structures are constructed such that substantially all of the strength of the packaging structure is provided by the kraft strength layer or layers. Modest contribution may be obtained from the polymeric layer. The outer graphics layer contributes essentially no net increment to strength of the packaging structure. In other words, the graphics layer could be deleted without substantial loss of strength of the packaging structure. However, such deletion would undesirably delete the graphics contribution of the outer graphic layer.
The graphics and/or printed indicia presentation on the outer surface of the outer layer serves multiple purposes. First, the printing can serve as a point-of-sale advertising medium. Second, the printing can be used to satisfy certain government regulations which require identification of certain attributes of the goods. In addition, the printing can serve to draw initial attention to the package. Thus, it is critical to both buyer and seller of such packaged goods that the printing remain intact, as printed, on the outer surface of the packaging structure at least throughout the period when the goods are contained in the package.
It is well known that such printing is readily degraded, in some cases rendered useless, by certain oils, for example vegetable and grain oils. For example, the oils present in commercially available dry dog food and dry cat food, inside a closed and sealed bag, can have damaging affect on the printing which is on the outside surface of the bag. Thus, it is known to provide certain barriers to transmission of such oils through the packaging material to the printed indicia and the coatings under the printed indicia. It is known, for example, to provide a layer of e.g. about 0.005 inch thick polyolefin such as polypropylene or polyethylene as the innermost layer of the packaging structure, namely as an interior surface layer at the cavity which contains the product. Such polyolefin layer serves as a first barrier to migration of such oils toward the print coating.
In order to ensure protection of the print coating, the substrate to be printed as the outer layer of the packaging material is typically saturated with fluorocarbon, wherein the fluorocarbon serves as a final barrier to migration of the oils toward the printed indicia as well as the underlying print coating. However, government regulations require that users discontinue such uses of fluorocarbon. Further, saturating the substrate with fluorocarbon uses a substantial quantity of the fluorocarbon barrier material. By comparison, a barrier material which is concentrated at the surface of the substrate layer, such as by a coating process, can potentially use less of the barrier material.
It would be desirable for the layer which provides the graphics presentation to also contribute to strength. Stated another way, it would be desirable to provide graphics capability to a strength layer. Stated still another way, it would be desirable to combine graphics and strength properties in a common layer, thereby saving the cost of using a layer, which contributes no substantial amount of the strength, for the purpose of presenting the graphics message. Namely, if the graphics message can be provided in a layer which also provides a substantial strength increment to the packaging structure, the quantity of paper used in the packaging structure can be reduced by the incremental amount of paper which would otherwise be used to present the graphics message.
Thus, it is an object of the invention to provide flexible packaging material for packaging bulk bagged product, especially particulate product, wherein the packaging material tolerates the use conditions of the packaged goods contained therein while improving cost efficiency of the packaging material.
It is a more specific object to provide packaging material which is flexible throughout its use for containing a product therein, while maintaining printed indicia thereon in good condition throughout the term of use of the package.
It is yet another object of the invention to provide flexible packaging structures wherein the printed indicia tolerates repeated flexing of the packaging material without damage to the printed indicia or the message conveyed by such indicia.
It is yet another object to provide packaging material having a novel second barrier to oil migration, on the reverse surface of the layer which bears the printed indicia.
Still another object of the invention is to provide a coated sheet material which has a surface suitably receptive to receiving conventional printing inks, and which is coated onto a substrate which provides substantial contribution toward the strength of the packaging material, and which can preferably serve as a primary strength layer.
A further object is to provide such coated sheet material wherein the substrate sheet which provides primary strength contribution, in combination with a suitable ink-receptive printing surface, is a sheet of unbleached kraft paper.
A yet more specific object is to provide such coated printable unbleached kraft paper wherein the suitably receptive surface is suitably white to meet conventional printing standards pertaining to suitability of a white surface onto which conventional colored inks can be effectively printed with reasonable expectation of desirable color and clarity presentations.
Yet another object is to provide, on relatively open and porous paper substrates, novel barrier coatings which can serve as a final barrier, in combination with an initial polyolefin film barrier layer, to migration of certain oils toward a print coating, thus to protect the print coating from the deleterious affect of the oil.